Chemistry Reference
In-Depth Information
net 4Fe
2
O
2
ÿ! 4Fe
3
2HO
ÿ
2H
2.4
2H
Fe
3
H
2
O
2
Our work (Harel, 1994) showed that 100M of ferrous sulfate was oxidized
during interaction of 50M of H
2
O
2
with 200M of FeSO
4
at pH7.0 buffer
acetate. This could be explained only if ferrous ions react by equations 2.3
and 2.4. The same stoichiometric ratio of Fe
2
/H
2
O
2
of 2:1 was shown by
Qian and Buettner (1999) to prevent oxidation of target molecules by HO
·
.
3. The most important reason to consider the oxidative chemistry initiated by
Fe
2
O
2
as a significant route to biological oxidation is that the overall
steady state concentration of oxygen is much greater, about 10
3
higher than
pre-existing H
2
O
2
in living systems (O
2
, 10M and H
2
O
2
, 10 nM). Data
demonstrated by Qian and Buettner (1999) showed that when [O
2
]/[H
2
O
2
]
>100, Fe
2
O
2
chemistry is an important route to initiation of detrimental
biological free radical oxidation, much more than Fe
2
with pre-existing
H
2
O
2
(Fenton reaction). This chemistry leads to the formation of ferryl ion
from loosely bound iron by the following reactions:
Reaction 2.1 will generate Fe
3
O
2
·ÿ
which further generate a complex
between Fe
2
and O
2
.
Fe
3
O
2
·ÿ
Fe
2
O
2
·ÿ
ÿÿÿ!
ÿ! Fe
2
-O
2
2.5
Fe
2
-O Fe
2
ÿ! Fe
2
-O
2
±Fe
2
2.6
Fe
2
-O
2
±Fe
2
ÿ! 2Fe
4
=O oxo-ferryl ion
2.7
However, fresh muscle tissue after slaughtering and grounding at 37 ëC
generates H
2
O
2
at a very significant amount of about 0.9 nmole/g min and
after 60 min produce a steady state concentration of abut 50M (Kanner and
Harel, 1985b; Jorgenson and Skibsted, 1998; Harel and Kanner, 1985a).
Aging muscle tissues at 4 ëC for a period of 5 days increases H
2
O
2
production
almost 2.3 fold. It seems that in muscle foods, endogenous generation of
H
2
O
2
plays an important role in the formation of the primary pool of
biological catalysts.
4. Reducing agents are the most important co-factors turning transition metals
such as Fe or Cu ions into significant catalysts of non-enzymic oxidation in
biological and food systems. The most active reducing compounds involved
in such reaction are ascorbic acid, cysteine, polyphenols, protein-SH,
NADPH, NADH and dopa, dopamine and other minor reducing agents. We
could assume that nearly all `loosely bound' or catalytic iron is present as
Fe
2
(Keyer and Imlay, 1996).
The interaction between ascorbic acid and transition metals could be
described by the following reaction:
Fe
3
/Cu
2
2AH
2
ÿ! Fe
2
/Cu
1
2AH
·
2H
2
2.8
AH
·
AH
·
ÿ! AH
2
A
2.9
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